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vmware-tanzu-labs/object-code-generator-for-k8s

This project extends the hard work put in by the VMware Tanzu Labs team to originally create this utility. It extends the functionality of the original intent of generating Go code to generating other various items for Kubernetes.

Object Code Generator for K8s

Generate source code for unstructured Kubernetes Go types from yaml manifests.

This project is intended for use when scaffolding source code for Go projects that manage Kubernetes resources.

It can be used in two ways:

1. Imported and used as a package
2. Installed and used as a CLI

Package

The primary use is as an imported package. Import the generate package and use it to generate an unstructured Kubernetes object from a yaml manifest.

package main

import (
    "fmt"
    "io/ioutil"

    "github.com/nukleros/gener8s/pkg/generate"
)

func main() {

    manifestYaml, err := ioutil.ReadFile("path/to/yaml/file")
    if err != nil {
        panic(err)
    }

    object, err := generate.Generate(manifestYaml, "varName")
    if err != nil {
        panic(err)
    }

    fmt.Println(object)
}

See cmd/gener8s/main_test.go for a more complete example that uses templating to create a Go program that will create a Kubernetes deployment resource in a cluster.

Command Line Interface

You can also install and use as a CLI.

Install:

make install

Generate object source code from one or more yaml manifests:

gener8s go --manifest-files path/to/manifests/*.yaml --variable-name varName

Templating

You can also resolve templating within the manifests, values may be given via the optional values parameter or with the -f flag when using the CLI. This can be useful when dealing with multiple layers of code generatation, or for generating code with variable references.

Variable References

Sometimes you may want to generate code with variable references. To tell the generator a value is a variable, you may use a special !!var yaml tag on that value.

Variable Reference Inside a string

Sometimes to may want to generate code with a variable reference inside a string. To tell the generator a value contains a variable inside it. Inside the value you may the special tags !!start to mark the start of the variable and !!end to mark the end. the generator will automatically interpolate these and escape quotation marks appropriately

Example

in this example we will combine templating, variables, and nested variables. Note that all these features are optional. They can be used independently, together, or not at all.

Example manifest:

apiVersion: apps/v1
kind: Deployment
metadata:
    name: '{{ .Name }}'  # template variable
spec:
    replicas: 2
    selector:
        matchLabels:
            app: !!var webstoreLabel  # variable reference
    template:
        metadata:
            labels:
                app: '{{ .Label }}'  # templated reference
        spec:
            containers:
              - name: webstore-container
                image: my.private.repo/!!start image !!end  # nested variable reference
                ports:
                  - containerPort: 8080

Example values file:

Name: MyName
Label: webstoreLabel
Image: variable.With.Image.Value

This manifest and values file will produce:

var test = &unstructured.Unstructured{
	Object: map[string]interface{}{
		"apiVersion": "apps/v1",
		"kind":       "Deployment",
		"metadata": map[string]interface{}{
			"name": "MyName",
		},
		"spec": map[string]interface{}{
			"replicas": 2,
			"selector": map[string]interface{}{
				"matchLabels": map[string]interface{}{
					"app": webstoreLabel,
				},
			},
			"template": map[string]interface{}{
				"metadata": map[string]interface{}{
					"labels": map[string]interface{}{
						"app": webstoreLabel,
					},
				},
				"spec": map[string]interface{}{
					"containers": []interface{}{
						map[string]interface{}{
							"name":  "webstore-container",
							"image": "my.private.repo/" + variable.With.Image.Value + "",
							"ports": []interface{}{
								map[string]interface{}{
									"containerPort": 8080,
								},
							},
						},
					},
				},
			},
		},
	},
}

Testing

Testing changes to this project involves generating source code for a deployment resource, then installing that resource in a Kubernetes cluster. You will need to have the KUBECONFIG env var set that points to a valid kubeconfig for a running cluster.

Generate source code and run to install deployment in default namespace:

make test.run

Verify the deployment was successfully installed:

make test.verify

Note that this only verifies the deployment was installed. You may still need to validate the deployment created includes all intended fields.

Clean up the test deployment:

make test.clean